An injector includes a syringe in which an injection component (an injection objective substance) is encapsulated. The injector drives a piston with respect to the injection component to eject the injection component. There is an injector that supplies, with, for example, pressure by a pressurized gas, a spring, combustion by an explosive component or the like, force for driving the piston.
For example, an injector disclosed in Patent Literature 1 is an injector actuated by a propellant. An internal shell and a chemical unit are incorporated in a main body. The propellant is disposed in the internal shell and stored in an external shell together with the chemical unit. The external shell is fit in the main body and covered with a cover. Chemical is ejected by combustion of the propellant. An injector disclosed in Patent Literature 2 is an injector of a handgun type. A part (the peripheral surface) of a main body is opened. A cartridge is inserted from this opening section. The cartridge includes a piston, a bellows section, in which chemical is stored, and a nozzle. In the injector, the chemical is ejected by the force of a spring.